Research Program: My research is focused on the physiological and
behavioral ecology of pinnipeds, seals and sea lions.
My approach is to integrate physiology and behavior with the aim of addressing
ecological theory. I am investigating physiological factors that impact the
reproductive and foraging strategies used by marine predators. Much of my
current research is focused on the physiology and behavior of northern elephant
seals. These investigations include both field and laboratory studies. My field
research focuses on studies of fasting physiology and reproduction when seals
are hauled out on land to breed and diving physiology and foraging when animals
are at sea. My graduate students are exploring a wide variety of research
areas including fasting physiology, foraging behavior and life history strategies.
My lab has a strong collaborative relationship with the Institute
of Marine Sciences at the University
of California, Santa
Cruz.

Recent Work

Fasting Physiology

This work is sponsored by NSF in collaboration with Dorian
Houser and Cory Champagne from the National Marine Mammal Foundation and
others. We investigate the metabolic adaptations that allow animals to go for
weeks and months without food and water while undergoing costly activities like
breeding. These studies use cutting edge metabolic tracer technologies and 'omics approaches to better understand the regulation of
metabolism under the constraints of extreme fasting and include investigations
of the endocrine regulation of fasting.

We've found that, unlike other animals, elephant seals maintain
high rates of glucose production while fasting, mainly by recycling glucose
carbon through the Cori Cycle in association with high rates of pyruvate and
TCA cycle activity. These features allow elephant seals to provide fuel for
glucose dependent tissues while maintaining high rates of fat oxidation without
significant accumulation of ketoacids or use of
protein from vital organs. These unusual features allow elephant seals to
exhibit some of the highest sustained metabolic rates during fasting found in
nature.

Conservation
Physiology

This work is sponsored
by the Office of Naval Research in collaboration with Dorian Houser and Cory Champagne from the National Marine Mammal
Foundation and others. We are investigating the endocrine stress responses of
marine mammals and how they vary with foraging success, fasting and
life-history stage. We are examining the interaction of stress responses with
the reproductive and immune systems to better understand how stress has
demographic impacts. Our ultimate goal is to better understand how organisms
respond to climate variability and anthropogenic stressors and how these
responses integrate with the stress associated with breeding. These
investigations include the regulation of natality and
breeding behavior by reproductive hormones and impacts of breeding on the
immune system.

Foraging Ecology

This work is sponsored by NSF
and many others.In collaboration with Dan
Costa's lab at UCSC, my lab participates in the Tagging of Pacific Predators
(TOPP) project. My interest is in the foraging strategies used by elephant
seals and other marine predators and how these strategies vary with intrinsic
state variables (like mass or age) and ocean climate. These studies also
integrate with our conservation physiology research which seeks to understand
how foraging effort and success influences reproductive effort, stress and
health. These studies have also included work on the foraging behavior of
several Antarctic pinnipeds and their responses to
the rapidly changing climate.

Oxidative Stress and Metabolic
Syndrome

This work is sponsored by NIH in
collaboration with Rudy Ortiz from UC, Merced. We are investigating the
oxidative stress defenses of elephant seals that allow them to survive extended
breath-holds and fasting without oxidative damage. We are also studying the
adaptations that allow elephant seals to maintain diabetic-like features
including insulin insensitivity without harmful effects. Our goal is to not
only understand the physiological adaptations of the seals but also to inform
our understanding of oxidative stress and metabolic pathologies in humans.

Diving Physiology and Development

This work is sponsored by NSF and
NIH and seeks to understand the physiological adaptations that allow marine
vertebrates to hold their breath for extended periods while exercising. These
investigations include the development of diving physiology in elephant seals
and its impact on the foraging strategies used by juveniles.